Chemistry Reference
In-Depth Information
Archaeological Wood
Most ancient wooden objects recovered in archaeological excavations are
usually in a decayed, weak, and friable condition that requires stabilization
before the objects can be safely handled and studied. Stabilization of wood
and decayed wooden objects, generally includes the use of
consolidants
,
liquid solutions of a resin that impregnates and fills gaps in the wood
and on drying solidifies, strengthening its fragile, deteriorated structure
(Thompson 1991; Rowell and Barbour 1990).
Of particular interest in archaeological studies is
waterlogged wood
, wood
that has been submerged in water or buried in very wet soil for long periods
of time. When submerged in water, wood undergoes chemical and biologi-
cal processes that, at an advanced stage, leave it with very little solids, con-
taining more water than the total mass of dry matter (Jensen and Gregory
2006). Waterlogged wood is, therefore, very soft and mechanically weak,
retaining its shape only as long as it remains wet. If removed from the site
where it was submerged or buried and then exposed to the atmosphere, the
water soon evaporates and, as the wood dries, it undergoes severe dimen-
sional changes. This introduces internal stresses that further reduce the
strength of the wood, which develops cracks, cause flaking and may even
result in the total breakdown of the wood. The preservation of waterlogged
wood removed from a wet environment requires, therefore, specialized treat-
ment beginning even before removal from the submersion or burial site
(Jordan 2001; Grattan and McCawley 1981).
9.2.
GUMS
Gums
are complex carbohydrates exuded from plants, or produced by the
decomposition of vegetable matter, that have been used since remote times
as
adhesives
,
sizes
, and
binders
(see Table 73). Most gums are tasteless and
odorless solids that either dissolve or swell in water to form adhesive,
viscous mucilages. When the water evaporates from a mucilage, the
TABLE 73
Natural Gums
Gum
Source
Gum arabic
Acacia segalencis and other acacia trees, native to eastern Africa
Gum kadaya
Sterculia urens trees from India
Locust bean
Seeds of carob (Ceratonia siliqua) trees
Tamarind
Seeds of tamarind (Tamarindus indica) trees
Tragacanth
Astragalus gummifer shrubs from southern Europe and the
Middle East
